Corrosion patterns and optimal materials of tubings in sulfur purification buried wells in the Sichuan Basin

The study aims to explore the corrosion behaviors of tubings of different materials under the injection condition of sulfur-containing purification exhaust gas buried storage well and select a proper steel. A high-temperature and high-pressure autoclave was used to simulate the injection condition of sulfur-containing purification exhaust gas and carry out corrosion weight loss tests on N80 carbon steel, 13Cr stainless steel, and 825 nickel-based alloy steel under two different partial pressures of CO₂ (2 and 5 MPa). Corrosion rate, the morphology of corrosion products, the morphology of cross-section of corrosion products, and local corrosion depth were explored and the corrosion life prediction and economic evaluation of tubings were performed. Under the simulated conditions, with the increase in CO₂ partial pressure, the corrosion rates of N80 carbon steel, 13Cr stainless steel, and 825 nickel-based alloy steel increased from 0.0548 mm/a, 0.0172 mm/a, and 0.0013 mm/a to 0.102 mm/a, 0.025 mm/a, and 0.0034 mm/a. The corrosion products of the three steels were mainly FeCO₃ and FeS and gradually increased with the increase in CO₂ partial pressure. However, the connection among corrosion products was not dense and cracks and holes were observed in the corrosion product film. N80 steel mainly exhibited the uniform corrosion and its residual tensile strength and tensile safety factor decreased with the increase in service life. Safe service life decreased from 48a to 26a with the increase in CO₂ partial pressure. Pitting corrosion occurred in 13Cr steel and the ultimate perforation life decreased from 6.05a to 3.36a with the increase in CO₂ partial pressure. Based on the consideration of economy and field applicability, N80/825 bimetal composite tubing is recommended as the material of tubings.